Methods and apparatus for an adjustable stiffness catheter

ABSTRACT

Apparatus and methods for an endovascular catheter that can be inserted within tortuous body anatomies and then selectively stiffened and fixed in place. In a particular embodiment, this stiffness is reversible. The stiffness or a comparable mechanical characteristic of the catheter assembly may be adjusted to a relatively low value during insertion (so that it easily navigates a guide wire or the like), and then subsequently adjusted to a relatively high value in situ to keep the catheter assembly substantially fixed in place (i.e., during delivery of an interventional device).

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the priority benefit under 35 U.S.C. §119(e) ofU.S. Provisional Application No. 61/430,303 filed on Jan. 6, 2011, thecontent of which is incorporated herein in its entirety.

TECHNICAL FIELD

Embodiments of the subject matter described herein generally relate tocatheter systems, and more particularly relate to catheters of the typeused in the context of tortuous anatomic features.

BACKGROUND

Catheters are useful in performing a wide range of medical procedures,such as diagnostic heart catheterization, percutaneous transluminalcoronary angioplasty, and various endocardial mapping and ablationprocedures. It is often difficult, however, to selectively catheterizecertain vessels of the human body due to the tortuous paths that thevessels follow. FIG. 1, for example, is a conceptual diagram useful indepicting the human aortic arch 100. As shown, the ascending aorta 110rises from its origin at the aortic valve (not shown). The right commoncarotid 104 and the right subclavian 103 branch off of thebrachiocephalic artery 102. The left common carotid 105 and the leftsubclavian artery 106 branch and rise from the aorta just before itturns and descends to the descending aorta 120. Dashed line 170 depictsa typical catheter placement that might be desirable in this context.

Normal aortic arches such as that shown in FIG. 1 rarely requireintervention. Instead, interventionalists most often find themselvesviewing and navigating diseased and abnormal aortic pathology, such asthat shown in FIGS. 2A-2D, which depict assorted variant conditions ofthe human aortic arch (201-204). It is clear that navigation from thedescending aorta 120, up over the arch, and then back to gain access tothe right brachiocepalic artery 102 can be extremely difficult in suchcases, particularly when the arteries are partially occluded with easilydisplaced and dislodged build-ups of plaque.

As a result, catheterization procedures often require multiple catheterexchanges—i.e., successively exchanging catheters with different sizesand/or stiffness to “build a rail” through which subsequent catheterscan be inserted, eventually resulting in a wire and guide stiff enoughto allow delivery of the intended interventional device (e.g., a stent,stent-graft, or the like).

Flexibility is therefore desirable in a catheter to allow it to trackover a relatively flexible guidewire without causing the guidewire topull out. That is, the “navigatibility” of the catheter is important. Atthe same time, the stiffness or rigidity of the same catheter isdesirable to allow the guiding catheter to be robust enough to allow arelatively stiff device (such as a stent) to be tracked through theguiding catheter without causing the guiding catheter to lose position(i.e., becoming “dislodged”). If dislodgement occurs, the entireprocedure of guide wire and guide catheter exchanges must be performedagain from the beginning.

Often, an optimal balance is sought, such that the distal end of thecatheter is flexible, and the proximal end is stiff to enable tracking.However, in order to move the stiff part of a catheter in place, theflexible section typically needs to be buried deep within the anatomy toget “purchase” and to hold position. In many instances, the anatomy doesnot allow for deep purchase. Accordingly, there is a need for catheterdesigns and methods that overcome these and other shortcomings of theprior art.

SUMMARY OF THE INVENTION

The present invention generally relates to a catheter assembly having anadjustable stiffness during, for example, endovascular procedures withinthe human body. That is, the stiffness or a comparable mechanicalcharacteristic of the catheter assembly may be adjusted to a relativelylow value during insertion (so that it easily navigates a guide wire orthe like), and then subsequently adjusted to a relatively high value insitu to keep the catheter assembly substantially fixed in place (i.e.,during delivery of an interventional device).

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a conceptual diagram depicting a human aortic arch useful indescribing the present invention;

FIGS. 2( a)-(d) depict various common aortic pathologies;

FIG. 3 is a conceptual cross-sectional diagram depicting a catheterapparatus in accordance with one embodiment;

FIGS. 4 and 5 are qualitative graphs showing the value of a stiffnessmetric as a function of length for catheters in accordance with variousembodiments;

FIG. 6 depicts a three-point bend test used for measuring a stiffnessmetric;

FIGS. 7( a)-(c) depicts an alternate test used for measuring a stiffnessmetric;

FIGS. 8( a)-(b) depicts a catheter apparatus in accordance with oneembodiment;

FIG. 9 depicts a catheter apparatus in accordance with one embodiment;

FIGS. 10( a)-(b) and 11 depict a catheter apparatus in accordance withone embodiment;

FIGS. 12-13 depict a catheter apparatus in accordance with oneembodiment;

FIGS. 14-15 depict a catheter apparatus in accordance with oneembodiment;

FIGS. 16-17 depict a catheter apparatus in accordance with oneembodiment;

FIGS. 18( a)-(c) depicts lumen configurations in accordance with variousembodiments; and

FIG. 19 depicts a qualitative graph showing the value of a stiffnessmetric in accordance with one embodiment.

DETAILED DESCRIPTION Overview

Referring to the longitudinal cross-section shown in FIG. 3, a catheterapparatus (or simply “catheter”) 300 in accordance with one embodimentgenerally includes a generally tubular body (or simply “body”) 304having a delivery lumen (or simply “lumen”) 301 defined therein.Catheter 300 extends from a distal end 308 (generally, the endconfigured to be inserted first within an anatomical feature) and aproximal end 310 opposite distal end 308. A controller 320communicatively coupled to catheter body 304 and/or lumen 301 will alsotypically be provided for controlling the operation of catheter 300, asdiscussed in further detail below.

An activation means (not illustrated in FIG. 3) is provided for causingbody 304 to enter two or more states, which may be discrete states orstates that vary continuously, or a combination thereof. The activationmeans will generally include a variety of mechanical, pneumatic,hydraulic, electrical, thermal, chemical, and or other components asdescribed in connection with the various embodiments presented below,and may be incorporated into body 304, lumen 301, controller 320, or acombination thereof. In various embodiments, controller 320 is onecomponent of the activation means.

In general, body 304 can be selectably placed in at least two states. Inthe first state, body 304 has a relatively low stiffness and/or hasother mechanical properties selected such that catheter 300 can easilybe inserted (e.g., via manual axial force applied at proximal end 310)over a guide wire or the like without substantially disturbing theplacement of that guide wire. A variety of conventional, commerciallyavailable guide wires are known in the art, and need not be discussed indetail herein. In the second state, body 304 has a relatively highstiffness and/or other has mechanical properties selected such thatcatheter 300 remains substantially in place within the anatomicalfeature during subsequent operations, including the removal of any guidewire used during insertion. Stated another way, while in the firststate, body 304 has a stiffness metric that is equal to or less than apredetermined “navigatibility threshold,” and while in the second state,body 304 has a stiffness metric that is greater than or equal to apredetermined “rigidity threshold.” This is illustrated in FIG. 19,which qualitatively depicts two states (1902 and 1904) and theircorresponding stiffness threshold values (i.e., navigatibility thresholdand rigidity threshold, respectively).

The term “stiffness metric” as used herein refers to a dimensionless ordimensional parameter that may be defined in various ways, as describedin further detail below. However, regardless of the nature of thestiffness metric, the navigatibility threshold and rigidity thresholddefine the primary modes of operation of catheter 300. In this regard,note that “stiffness metric” is often used herein to refer to an actualstiffness metric value.

Stiffness Metric and Thresholds

FIG. 4 presents a qualitative graphical representation of a stiffnessmetric (S) as a function of distance along catheter 300 from itsproximal end to its distal end. FIG. 4 corresponds to the case where thestiffness metric is substantially uniform along its length, but as willbe seen below, the invention is not so limited. Dashed line 412indicates the navigatibility threshold, and dashed line 410 representsthe rigidity threshold for a given stiffness metric. While in the firststate (during insertion) catheter 300 has a stiffness metric 402 that isequal to or less than navigatibility threshold 412. Similarly, while inthe second state, catheter 300 has a stiffness metric 410 that isgreater than or equal to rigidity threshold 410.

In one embodiment, the stiffness metric corresponds to the flexuralmodulus of catheter 300—i.e., the ratio of stress to strain duringbending, as is known in the art. This value may be determinedempirically, for example, using a three-point bend test as shown in FIG.6, wherein catheter 300 (or a portion of catheter 300) is placed on apair of supports 602 and 604 that are a known distance apart, and adownward (radial) force 608 is applied to catheter 300 via a thirdstructure 606 that is situated between supports 602 and 604.

In another embodiment, the stiffness metric corresponds to an empiricalmeasurement that more closely models the actual operation of catheter300. For example, FIGS. 7( a)-(c) depict a “dislodgment” test thatsimulates the placement of a catheter 300 placed at approximately a90-degree angle (although this angle may vary depending upon the test).More particularly, stationary supports 702, 704, and 706 are positionedin a predetermined geometric relation such that catheter 300 (or a shortsegment cut from catheter 300) must bend to fit between supports 702 and704 while contacting support 706. Additional supports (not illustrated)may also be used to assist in placing catheter 300.

During the start of the test, a probe 702 is inserted within one end ofcatheter 300 as shown (FIG. 7( a)). Probe 702 might be configured toapproximate the stiffness of a typical stent-graft or the like. As probe702 is further inserted into the lumen 301 of catheter 300, it makescontact with the inner surface of the lumen 301 and causes end 308 tomove with respect to support 702. Ultimately, when probe 702 is insertedwith a sufficient force, catheter 300 will be released entirely frombetween supports 702 and 704 as shown. The force necessary to dislodgecatheter 300 in this way then becomes the stiffness metric. The test isadvantageously conducted at approximately 37° C. (body temperature).Further, the test may be initiated with an exemplary guide wire inplace, thereby allowing the navigatibility threshold to be determined.

Stiffness Metric Variation

While FIG. 4 depicts the stiffness metric as being invariant over thelength of catheter 300, the invention is not so limited. FIG. 5 presentsa qualitative graphical representation of stiffness metric (S) as afunction of distance along catheter 300 from its proximal end to itsdistal end; however, in this embodiment, catheter 300 includes two“zones” or segments, each having a corresponding stiffness metric whilein the second state. That is, in zone 520, the stiffness metric in thesecond state (504) is substantially the same as the stiffness metric inthe first state (502) (i.e., is generally below the navigatibilitythreshold 412). Within zone 522, the stiffness metric in the secondstate (504) is above the rigidity threshold 410.

Catheter 300 may include any number of such zones. Furthermore, thestiffness metric within each zone may be constant or vary continuously.In a particular embodiment, a first zone is adjacent to the distal endof catheter 300, and a second zone is adjacent to the first zone,wherein the stiffness metric of the first zone is less than thestiffness metric of the second zone while in the second state.

In an alternate embodiment, catheter 300 has one stiffness metric valuealong a first curvature axis and another stiffness metric value along asecond curvature axis that is orthogonal to the first curvature axis.

Catheter Body

Catheter body 304 may have any suitable structure, and be fabricatedusing any suitable combination of materials capable of achieving theselectable stiffness metric described above. For example, in oneembodiment, catheter body 304 includes a helical (spiral) channel formedwithin its exterior and/or its interior. The channel effectively weakensbody 304 such that the stiffness metric in the first state is lower thanit would be if the body 304 were perfectly tubular. In anotherembodiment, catheter body 304 includes a plurality of ring-shapedchannels formed circumferentially therein. In a particular embodiment,the plurality of ring-shaped channels are distributed irregularly alongthe tubular body. Such an embodiment allows the baseline stiffnessmetric to vary in a specified way along the length of catheter 300.

Catheter body 304 may comprise a variety of materials. Typical materialsused to construct catheters can comprise commonly known materials suchas Amorphous Commodity Thermoplastics that include PolymethylMethacrylate (PMMA or Acrylic), Polystyrene (PS), AcrylonitrileButadiene Styrene (ABS), Polyvinyl Chloride (PVC), Modified PolyethyleneTerephthalate Glycol (PETG), Cellulose Acetate Butyrate (CAB);Semi-Crystalline Commodity Plastics that include Polyethylene (PE), HighDensity Polyethylene (HDPE), Low Density Polyethylene (LDPE or LLDPE),Polypropylene (PP), Polymethylpentene (PMP); Amorphous EngineeringThermoplastics that include Polycarbonate (PC), Polyphenylene Oxide(PPO), Modified Polyphenylene Oxide (Mod PPO), Polyphenelyne Ether(PPE), Modified Polyphenelyne Ether (Mod PPE), Polyurethane (PU),Thermoplastic Polyurethane (TPU); Semi-Crystalline EngineeringThermoplastics that include Polyamide (PA or Nylon), Polyoxymethylene(POM or Acetal), Polyethylene Terephthalate (PET, ThermoplasticPolyester), Polybutylene Terephthalate (PBT, Thermoplastic Polyester),Ultra High Molecular Weight Polyethylene (UHMW-PE); High PerformanceThermoplastics that include Polyimide (PI, Imidized Plastic), PolyamideImide (PAI, Imidized Plastic), Polybenzimidazole (PBI, ImidizedPlastic); Amorphous High Performance Thermoplastics that includePolysulfone (PSU), Polyetherimide (PEI), Polyether Sulfone (PES),Polyaryl Sulfone (PAS); Semi-Crystalline High Performance Thermoplasticsthat include Polyphenylene Sulfide (PPS), Polyetheretherketone (PEEK);and Semi-Crystalline High Performance Thermoplastics, Fluoropolymersthat include Fluorinated Ethylene Propylene (FEP), EthyleneChlorotrifluroethylene (ECTFE), Ethylene, Ethylene Tetrafluoroethylene(ETFE), Polychlortrifluoroethylene (PCTFE), Polytetrafluoroethylene(PTFE), Expanded Polytetrafluoroethylene (ePTFE), PolyvinylideneFluoride (PVDF), Perfluoroalkoxy (PFA). Other commonly known medicalgrade materials include elastomeric organosilicon polymers, polyetherblock amide or thermoplastic copolyether (PEBAX), Kevlar, and metalssuch as stainless steel and nickel/titanium (nitinol) alloys.

The material or materials selected for catheter body 304 may dependupon, for example, the nature of the activation means used to effect atransition from the first state to the second state of operation.Catheter body 304 may be manufactured, for example, using conventionalextrusion methods or film-wrapping techniques as described in U.S. Pat.App. No. 2005/0059957, which is hereby incorporated by reference.Additional information regarding the manufacture of catheters may befound, for example, at U.S. Pat. No. 5,324,284, U.S. Pat. No. 3,485,234,and U.S. Pat. No. 3,585,707, all of which are hereby incorporated byreference.

Activation Means (Generally)

Catheter 300 includes activation means for causing body 304 to enter twoor more states as detailed above. The activation means may make use of avariety of physical phenomenon and be composed of any number ofcomponents provided within and/or communicatively coupled to catheter300, including for example, controller 320 as illustrated in FIG. 1. Thechange of state may be accomplished, for example, via mechanicalactivation, electrical activation, pneumatic activation, chemicalactivation, and/or thermal activation. Typically, activation will occursubsequent to catheter placement—i.e., in situ. Various specific typesof activation means will now be discussed below in conjunction theexemplary embodiments.

EMBODIMENT 1 Thermal Activation

In one embodiment, the activation means includes a controller 320communicatively coupled to body 304 as well features within body 304that are together adapted to place the body in the second state bysubjecting at least a portion of the catheter 300 to a reduction orchange in temperature.

Referring now to FIGS. 8 (a)-(b) in conjunction with FIG. 1, a catheter300 in accordance with one embodiment generally includes two auxiliarylumens or channels 802 and 804 that are interconnected (e.g., fluidlycoupled near a distal end) such that the coolant travels through body304. The channels 804 and 802 are separated, for example, by a membrane(such as an ePTFE membrane) 806.

After delivery of catheter 300 (during which it is in the first state),a coolant 805 such as liquid nitrogen is supplied to channel 804 (e.g.,via a coolant delivery system within controller 320), where it travelsparallel to lumen 301 along the length of (or a portion of) body 304. Asthe changes from liquid to gas at membrane 806, it cools body 304 aswell as membrane 806. The materials for catheter body 304 and/ormembrane 806 are selected that their stiffness increases as thetemperature is reduced. Exemplary materials include, for example,urethane and the like. As channel 804 is significantly smaller thanchannel 802, compressed gas 803 is allowed to expand as it passesthrough membrane 806 into channel 802.

As a result of heat transfer from the coolant, the coolant (in the caseof liquid nitrogen) changes to a gas phase and exits through channel802. In other embodiments, the coolant remains in liquid form duringoperation. Suitable coolants include, for example, chilled saline,liquid CO₂, liquid N₂, and the like. Other approved medical chillingmethods may also be employed.

EMBODIMENT 2 Axial Compression

Referring now to FIGS. 16 and 17 in conjunction with FIG. 1, in oneembodiment, the activation means includes controller 320 communicativelycoupled to the body 304 and components within body 304 that are adaptedto place body 304 in the second state by subjecting it to an increase inaxial compression.

As shown in FIG. 16, one or more tension lines 1602 may be used toselectively apply a compressive force to body 304. The tension lines1602 are attached at the distal end 308 of catheter 300 and areslideably received by corresponding accessory lumens 1402 that passthrough a series of body segments 1605. The accessory lumens 1402 arepreferably sized to allow the free axial movement of tension lines 1602.Depending upon the particular design, body segments 1605 will typicallybe separated by a small interstitial gaps 1607.

The tension lines 1602 are subjected to approximately zero tension(i.e., are generally “slack”) while navigating the anatomy during thefirst state; however, when stiffening of all or a portion of catheter300 is desired, tension lines 1602 are pulled substantiallysimultaneously as depicted in FIG. 17. Gaps and the orientation betweenbody segments 1605 may be optimized to reduce (and/or increase therepeatability of) the foreshortening that occurs when tension isapplied. In one embodiment, tension wires 1602 are attached to afloating gimbal mechanism incorporated into controller 320. Once tensionis applied, the compressive force tends to bind the catheter; therebydecreasing it's flexibility in that section. Reduction in the axiallength may accompany the application of tension. That is, asillustrated, the interstitial gaps 1607 may be reduced.

The tension lines may be made of any suitably strong and flexiblematerial, such as polymeric or metallic filaments or ribbons. The forcenecessary to place catheter 300 in the second state may vary dependingupon the length, material, and cross-section of tension lines 1602, aswell as the structural characteristics of body 304.

Any number of tension lines 1602 and accessory lumens 1402 may be used.FIGS. 18( a)-(c) present a cross-sectional view of various designs forcatheter body 304, including three equidistant accessory lumens 1402(FIG. 18( a)), two equidistant accessory lumens 1402 (FIG. 18( b)), andfour equidistant accessory lumens (FIG. 18( c)). In addition,equidistant accessory lumens may be distributed in any arbitraryfashion, and need not be symmetrical or equidistant as illustrated.

In one embodiment, the column stiffness of body 304 is modified to allowfor tracking, then increased to deployment without foreshortening duringstiffening.

EMBODIMENT 3 Radial Compression

In one embodiment, the activation means includes controller 320communicatively coupled to the body 304 and adapted to place the body304 in the second state by subjecting at least a portion of the tubularbody to an increase in radial compression. For example, body 304 mayinclude two fluid impermeable layers defining a pressure-responsivechamber and at least one interstitial structure provided within thepressure-responsive chamber. The controller is configured to cause achange in internal pressure within the pressure-responsive chamber; andthe interstitial structure is adapted to exhibit radial compression inresponse to the change in internal pressure.

Referring now to FIG. 9, in the illustrated embodiment catheter 300includes an accessory lumen 902 extending from chambers 906 to a hub302. Hub 302 in this embodiment is configured as a standard “Y” fitting,wherein negative pressure (i.e., a reduction from some baselinepressure) is applied be attaching a syringe to luer fitting 910. Whennegative pressure is applied, chambers 906 collapse and apply pressureto corresponding body segments 904 (as illustrated in FIGS. 12 and 13).The pressure is preferably great enough to cause a change in stiffnessmetric of the affected portion of catheter 300.

In an alternate embodiment shown in FIGS. 10A and 10B, the body 304comprises a layered structure 1002 (i.e., an interstitial component)positioned between two or more layers of an air-impermeable chamber1004. To facilitate the use of negative pressure, the chamber 1004includes a flexible polymeric material configured to be non-permeablewhile in the bloodstream. The flexible polymeric comprise, for example,Polyethylene Terephthalate (PET), Polyurethane, Fluorinated EthylenePropylene (FEP), Nylons or Flouropolymers, includingPolytetrafluoroethylene (PTFE) or Expanded Polytetrafluoroethylene(ePTFE), or combinations thereof.

At atmospheric pressure, bending causes the individual components oflayers 1002 to slide across each other with minimum friction. When theindividual layers are allowed to slide and act individually, theresulting stiffness metric is very low. Upon application of negativepressure, however, a normal (i.e., radial) force 1008 is created withinstructure 1002 by the collapse of the flexible polymeric material 1004.This normal force is translated through the layers, increasing thelayer-to-layer friction and limiting their ability to slide with respectto each other. As a result, the stiffness metric of the structure isincreased. In an alternate embodiment, the pressure is increased in anadjacent pressure chamber, thereby causing that chamber to press theadjacent layered structure.

The layered structure 1002 of the present invention may be manufacturedusing a variety of processes, including, for example, tape wrapping,braiding, serving, coiling, and manual layup. Suitable materialsinclude, include, fibers/yarns (Kelvar, nylon, glass, etc), wires (flator round, stainless steel, nitinol, alloys, etc), and/or thin slits offilm (Polyester, Nylon, Polyimide, Fluoropolymers including PTFE andePTFE, etc.) In this embodiment, the change in stiffness metric iseasily reversed by allowing the chamber pressure to increase (e.g., byrelaxation of a syringe attached to luer fitting 910), therebydecreasing the applied normal force.

In an alternate embodiment depicted in FIG. 11, multiple discrete airchambers 1102 are distributed along the length of catheter 300 and canbe toggled independently. Chambers 1102 may be composed ofdifferentiated layered structures, such as layers of slit, thin film1104. The distal air chambers may be controlled independently throughlumen 1109, while the proximal air chamber is controlled through lumen1108. This allows the operator to control the segments independently tovarying degrees of stiffness change. The lumens 1108 and 1109 may beconstructed in a variety of conventional ways, including evacuationthrough the annular space of the chamber, or individual lumens of tubingsuch as polyimide that either have an open end in communication with thehub, or holes through the sidewall allowing for unobstructed evacuation.

EMBODIMENT 4 Torsional Activation

In one embodiment, the activation means includes a controller rotatablycoupled to at least two body segments (i.e., portions of body 304),wherein controller 320 is configured to apply a relative rotationalforce between the body segments to cause the tubular body to enter thesecond state. In one embodiment, two body segments includes an outerlayer, an inner layer, and a torsionally-responsive structure providedtherebetween. In one embodiment, for example, the torsionally-responsivestructure comprises a substantially cylindrical braided structure.

EMBODIMENT 5 Solidifying Material/Membrane

In one embodiment, body 304 includes at least one inner chamber, aselectably solidifiable material provided within the inner chamber; anda controller fluidly coupled to the at least one inner chamber. Thesolidifiable material is adapted to substantially solidify in responseto, for example, UV radiation, the introduction of a catalyst within theinner chamber, a temperature change, the introduction of water (in thecase of hydrophilic particles), acoustic energy (in the case of anacoustically-active polymer), or an electrical current or field (in thecase of an electroactive polymer).

FIGS. 14 and 15 depict an exemplary embodiment incorporating aselectably solidifiable material to effect transition to the secondstate. As shown in FIG. 14, body 304 is at least partially filled with amedium 1404 (for example, within individual chambers as illustrated)that together can alter the stiffness metric of catheter 300. In thisembodiment, the medium 1404 is injected through accessory lumens 1402.Medium 1404 may be a substance that hardens relatively quickly, such asa silicone or polyurethane. If medium 1404 requires a catalyst toactivate, that catalyst may already reside within the walls of the body304 or within the material of catheter 300 itself.

In one embodiment, medium 1404 is a slurry of particles suspended insolution as depicted in FIG. 15. In this case, the walls of body 304 (ormembranes provided therein) may be selectively permeable so to allow acarrier liquid to escape (e.g., the chamber and/or catheter body walls)while confining the particles themselves. Once these particles build upand “pack” into the chamber they cause an increased stiffness metric inthat section. A variety of suitable particle materials and sizes can beused. In one embodiment, the particle possesses neutral buoyancy in theselected carrier liquid. A hydrophilic particle is advantageous in thatit swells during hydration, causing additional binding and increasedcatheter stiffness.

EMBODIMENT 6 Memory Metal

In one embodiment, the activation means includes at least one metallicstructure having shape-memory properties provided within body 304 andcommunicatively coupled to a power source (e.g. a voltage and/or currentsource located within controller 320). In one embodiment, theshape-memory metallic structure comprises a Ni/Ti alloy (nitinol).

CONCLUSION

What has been described are methods and apparatus for an endovascularcatheter that can be inserted within tortuous body anatomies and thenselectively stiffened and fixed in place. In a particular embodiment,this stiffness is reversible. In this regard, the foregoing detaileddescription is merely illustrative in nature and is not intended tolimit the embodiments of the subject matter or the application and usesof such embodiments. As used herein, the word “exemplary” means “servingas an example, instance, or illustration.” Any implementation describedherein as exemplary is not necessarily to be construed as preferred oradvantageous over other implementations. Thus, although severalexemplary embodiments have been presented in the foregoing description,it should be appreciated that a vast number of alternate but equivalentvariations exist, and the examples presented herein are not intended tolimit the scope, applicability, or configuration of the invention in anyway. To the contrary, various changes may be made in the function andarrangement of the various features described herein without departingfrom the scope of the claims and their legal equivalents.

Techniques and technologies may be described herein in terms offunctional and/or logical block components, and with reference tosymbolic representations of operations, processing tasks, and functionsthat may be performed by various computing components or devices.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

1. A catheter apparatus comprising: a tubular body having a distal end,a proximal end, and a lumen defined therein; and activation means forselectably causing the tubular body to enter a first state and a secondstate; wherein, in the first state, the tubular body has a first valueof a stiffness metric that is below a predetermined navigatibilitythreshold; and wherein, in the second state, the tubular body has asecond value of the stiffness metric that is above a predeterminedrigidity threshold value.
 2. A catheter apparatus comprising: a tubularbody having a distal end, a proximal end, and a lumen defined therein;and activation means for selectably causing the tubular body to enter afirst state and a second state; wherein, in the first state, the tubularbody has a first value of a stiffness metric; wherein, in the secondstate, the tubular body has a second value of the stiffness metric thatis greater than the first value; and wherein the activation meansincludes a controller communicatively coupled to the tubular body andadapted to place the tubular body in the second state by subjecting atleast a portion of the catheter apparatus to a reduction or change intemperature.
 3. A catheter apparatus comprising: a tubular body having adistal end, a proximal end, and a lumen defined therein; and activationmeans for selectably causing the tubular body to enter a first state anda second state; wherein, in the first state, the tubular body has afirst value of a stiffness metric; wherein, in the second state, thetubular body has a second value of the stiffness metric that is greaterthan the first value; and wherein the activation means includes acontroller communicatively coupled to the tubular body and adapted toplace the tubular body in the second state by subjecting at least aportion of the tubular body to an increase in axial compression.
 4. Thecatheter apparatus of claim 3, wherein the tubular body comprises aplurality of axial segments responsive to the increase in axialcompression.
 5. The catheter apparatus of claim 4, wherein thecontroller includes at least one linkage component mechanically coupledto at least one of the plurality of axial segments and extending to theproximal end of the tubular body.
 6. The catheter apparatus of claim 5,wherein the tubular body includes an auxiliary lumen provided therein,and wherein the at least one linkage component includes at least onewire component extending through the auxiliary lumen.
 7. The catheterapparatus of claim 6, wherein the tubular body includes at least twoauxiliary lumens distributed symmetrically within the tubular body. 8.The catheter apparatus of claim 7, wherein the at least one wireincludes two or more wires, and the controller includes a gimblecomponent coupled to the two or more wires, the gimble componentconfigured to apply substantially equal tension on the two or morewires.
 9. The catheter apparatus of claim 8, wherein the two or morewires includes four three wires.
 10. A catheter apparatus comprising: atubular body having a distal end, a proximal end, and a lumen definedtherein; and activation means for selectably causing the tubular body toenter a first state and a second state; wherein, in the first state, thetubular body has a first value of a stiffness metric; wherein, in thesecond state, the tubular body has a second value of the stiffnessmetric that is greater than the first value; and wherein the activationmeans includes a controller communicatively coupled to the tubular bodyand adapted to place the tubular body in the second state by subjectingat least a portion of the tubular body to an increase in radialcompression.
 11. The catheter apparatus of claim 10, wherein: thetubular body includes at least two fluid impermeable layers defining apressure-responsive chamber; the tubular body includes at least oneinterstitial structure provided within the pressure-responsive chamber;the controller is configured to cause a change in internal pressurewithin the pressure-responsive chamber; and the at least oneinterstitial structure is adapted to exhibit radial compression inresponse to the change in internal pressure.
 12. The catheter apparatusof claim 11, wherein the at least one interstitial structure includes aplurality of laminar members configured to be substantially slideablewith respect to each other during the first state, and be substantiallynon-slideable with respect to each other during the second state. 13.The catheter apparatus of claim 12, wherein the plurality of laminarmembers comprise a braid or a helically wrapped structure.
 14. Thecatheter apparatus of claim 10, wherein the tubular body includes anouter layer, an inner layer, and one or more interstitial structuresprovided therebetween; and wherein the controller includes at least onelinkage component mechanically coupled to at least one of theinterstitial structures and configured to cause the at least on linkagecomponent to expand and contract radially.
 15. The catheter apparatus ofclaim 12, wherein the at least one interstitial component comprises asubstantially cylindrical braided structure.
 16. The catheter apparatusof claim 12, wherein the at least one interstial component comprises ahelically-wrapped structure.
 17. A catheter apparatus comprising: atubular body having a distal end, a proximal end, and a lumen definedtherein; and activation means for selectably causing the tubular body toenter a first state and a second state; wherein, in the first state, thetubular body has a first value of a stiffness metric; wherein, in thesecond state, the tubular body has a second value of the stiffnessmetric that is greater than the first value; and wherein the tubularbody includes at least two body segments, the activation means includesa controller rotatably coupled to the at least two body segments, andthe controller is configured to apply a relative rotational forcebetween the at least two body segments to cause the tubular body toenter the second state.
 18. The catheter apparatus of claim 17, whereinthe at least two body segments includes an outer layer, an inner layer,and a torsionally-responsive structure provided therebetween.
 19. Thecatheter apparatus of claim 18, wherein the torsionally-responsivestructure comprises a substantially cylindrical braided structure.
 20. Acatheter apparatus comprising: a tubular body having a distal end, aproximal end, and a lumen defined therein; and activation means forselectably causing the tubular body to enter a first state and a secondstate; wherein, in the first state, the tubular body has a first valueof a stiffness metric; wherein, in the second state, the tubular bodyhas a second value of the stiffness metric that is greater than thefirst value; and wherein the tubular body includes at least one innerchamber, a selectably solidifiable material provided within the innerchamber; and a controller fluidly coupled to the at least one innerchamber.
 21. The catheter apparatus of claim 20, wherein thesolidifiable material is adapted to substantially solidify in responseto UV radiation.
 22. The catheter apparatus of claim 20, wherein thesolidifiable material is adapted to substantially solidify in responseto introduction of a catalyst within the inner chamber.
 23. The catheterapparatus of claim 20, wherein the solidifiable material is a polymeradapted to substantially solidify in response to a temperature change.24. The catheter apparatus of claim 20, wherein the solidifiablematerial includes hydrophilic particles configured to expand whencontacting water, and the controller is configured to introduce a volumeof water into the inner chamber.
 25. The catheter apparatus of claim 24,further including a perfusion lumen provided within the inner chamber,the perfusion lumen fluidly coupled to the controller.
 26. The catheterapparatus of claim 20, wherein the solidifiable material is anacoustically-active polymer.
 27. The catheter apparatus of claim 20,wherein the solidifiable material is an electroactive polymer (EAP). 28.A catheter apparatus comprising: a tubular body having a distal end, aproximal end, and a lumen defined therein; activation means forselectably causing the tubular body to enter a first state and a secondstate; and a controller adapted to selectably dispense an aqueousmixture; wherein, in the first state, the tubular body has a first valueof a stiffness metric; wherein, in the second state, the tubular bodyhas a second value of the stiffness metric that is greater than thefirst value; wherein the tubular body includes a chamber fluidly coupledto the controller and at least partially bounded by a membrane; andwherein the membrane is configured to be permeable to a liquid portionof the aqueous mixture and impermeable to a solid portion of the aqueousmixture.
 29. The catheter apparatus of claim 28, wherein the aqueousmixture is a saline mixture.
 30. A catheter apparatus comprising: atubular body having a distal end, a proximal end, and a lumen definedtherein; activation means for selectably causing the tubular body toenter a first state and a second state; and a controller comprising avoltage source; wherein, in the first state, the tubular body has afirst value of a stiffness metric; wherein, in the second state, thetubular body has a second value of the stiffness metric that is greaterthan the first value; and wherein the activation means includes at leastone shape-memory metallic structure provided within the tubular body andcommunicatively coupled to the voltage source.
 31. The catheterapparatus of claim 30, wherein the shape-memory metallic structurecomprises a Ni/Ti alloy.
 32. The catheter apparatus of claim 30, whereinthe stiffness metric is a measurement of the bending stiffness of thetubular body.
 33. The catheter apparatus of claim 30, wherein thestiffness metric is a catheter pull-out metric.
 34. The catheterapparatus of claim 30, wherein the tubular body has a plurality ofzones, each zone having a corresponding stiffness metric while in thesecond state.
 35. The catheter apparatus of claim 34, wherein, within afirst zone, the stiffness metric of the tubular body varies continuouslyalong its length while in the second state.
 36. The catheter apparatusof claim 35, wherein a first zone is adjacent the distal end of thetubular body, and a second zone is adjacent the first zone, furtherwherein the corresponding stiffness metric of the first zone is lessthan the corresponding stiffness metric of the second zone while in thesecond state.
 37. The catheter apparatus of claim 30, wherein, while inthe second state, the tubular body has the second stiffness value alonga first curvature axis and a third stiffness value along a secondcurvature axis that is orthogonal to the first curvature axis.
 38. Thecatheter apparatus of claim 30, wherein the activation means is coupledto a controller provided at the proximal end of the tubular body. 39.The catheter apparatus of claim 30, wherein the activation means iscommunicatively coupled to a controller configured to be slideablyinserted within the lumen.
 40. The catheter apparatus of claim 30,wherein the activation means is coupled to a controller that is remotefrom the tubular body.
 41. The catheter apparatus of claim 30, whereinthe tubular body includes a helical channel formed therein.
 42. Thecatheter apparatus of claim 30, wherein the tubular body includes aplurality of ring-shaped channels formed circumferentially therein. 43.The catheter apparatus of claim 42, wherein the plurality of ring-shapedchannels are distributed irregularly along the tubular body.